Being a kind of controlled-release preparation, the gastric remaining preparation offers the advantages of a reduced frequency of administration, sustained effective concentration, and mitigated side effects. In addition, the gastric remaining preparation is more or less indifferent to the gastric emptying rate so that the drug substance may be released in sufficient quantities at the absorption site. Therefore, any gastric remaining preparation is a very useful medical device and this is particularly true for those drug substances which are expected to act directly on the stomach or the upper part of the small intestine.
Among the hitherto-known gastric remaining preparations are the preparation exploiting a hydrophilic colloid (JP-A-58057315), the preparation comprising a hollow molded structure externally coated with an active substance (JP-A-55012411), the one utilizing foamable microcapsules (JP-A-52076418), the one comprising a mixture of a water-soluble polymer and an oil and fat with the specific gravity of the whole mixture having been controlled to not greater than 1 (JP-A-61043108, PCT WO91/06281), and the one comprising foamed ethylcellulose (JP-A-62145014), among others. While some of them are functionally acceptable gastric remaining preparations, many are intricate in structure and destroyed by the peristolic motion of the stomach to lose the expected floatability.
Meanwhile, the multi-screw extruder is a kind of screw kneading extruder which is quite different from the single-screw extruder in performance mode and application. Unlike the single-screw extruder which is a simple kneading extruder, the multi-screw extruder has a mechanism resembling an Archimedian screw pump which delivers a high energy output physically through the intermeshing and mutual interference of a plurality of screws, with the result that the load can be subjected to treatments not provided by the single-screw extruder. The multi-screw extruder has been elaborated chiefly in the food and plastics industries and is in common usage for the processing of food (cereals, protein, animal meat, fish meat, etc.) and the injection molding of plastics.
Technologies utilizing an extruder in the pharmaceutical field are disclosed in PCT WO92/18106, PCT WO093/01472, and JP-A-5194197, among other literature. These technologies are not concerned with intragastric resident preparations but are directed to pharmaceutical preparations differing from gastric remaining preparations in construction and effect.
Known in the field of food are several technologies by which swollen moldings are manufactured from certain food materials (e.g. starch materials) using a multi-screw extruder (JP-A-5284926, JP-A-5192083, JP-A-5023125, JP-A-4051849, JP-A-1252267, JP-A-61009253, etc.). However, these technologies are invariably designed to solve the problems characteristic of food industry (promotion of appetite, improvement of appearance, etc.) and belong to a different technical field.
Also known is a technology wherein a swollen molding called an interpenetrating polymer network structure composed predominantly of a lactic acid type polymer (e.g. polylactic acid) is provided by means of a screw extruder (JP-A-5177734). However, this swollen molding is designed for use as an absorbent or filter material for oil and body fluids. Moreover, swollen moldings of this type have a high affinity for water so that they are not adaptable to gastric remaining preparation.